Mathematical model describing the processes of mechanical stress development in response to strain of heterogeneous muscle fiber is created. The numerical algorithm to calculate viscoelastic properties of muscle fiber of arbitrary length is developed. In numerical experiments by the model it is shown that the local heterogeneity of geometrical and mechanical parameters of structural units of the model significantly influences in resulting mechanical response of whole fiber. Also it is established the close connection between parameters of mechanical and geometrical heterogeneity compensating each other. It is supposed that the mechanism may modulate the myocardial remodeling under changing load.